The invention relates to a method for controlling or regulating the pressure exerted on a material web in the nip between two cooperating rollers of a calender or the like having a roller loading device, and to a calender wherein the bearings of the lowermost roller are supported by a working cylinder which can be rapidly released from its roller supporting position and having a device for regulating the pressure exerted on a material web in the roller nip.
In conventional rolling mills for the compression treatment of webs, such as calenders and smoothing rollers, the pressure exerted on the material web in the roller nip cannot be precisely adjusted to a specific value, as in many cases would be desirable. This is true not only for embodiments in which in addition to the weight of the rollers a load is produced by the working cylinders supported against the lowermost roller, but also for embodiments in which the additional roller load is produced by working cylinders which press against the uppermost roller. It is true that in the latter instance the force acting as the additional load can be set with much more precision than in the first instance, where the working cylinders must also simultaneously produce the stroke force compensating for the weight of the roller aggregate. The additional load thus represents only a fraction of the entire stroke force of the operating cylinders. Lack of precision resulting from friction or a tilting of the slidably guided bearings, however, here, too, lead to deviations between the additional pressure prevailing in the roller nip and the additional roller load produced by the loading device. This lack of precision becomes most important when material webs are treated whose quality experiences significant impairment because of an incorrectly set pressure in the roller nip, resulting, for example, from a loss of volume which can appear in a paper web when the pressure in the roller nip is too high.